This application is based on and claims priority to Japanese Patent Application No. 2000-111549, filed Apr. 13, 2000, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention is directed to marine propulsion engines, such as outboard motors, and the exhaust systems therefor.
2. Description of Related Art
Outboard motors present a number of challenges to the designer. One such challenge is the very compact nature of an outboard motor. An outboard motor generally includes a powerhead that consists of a powering internal combustion engine and a surrounding protective cowling. A drive shaft housing and a lower unit depends from the powerhead. The drive shaft housing and lower unit journals a drive shaft that is driven by the engine. A transmission, which drives a propulsion device in the lower unit, thereby propels an associated watercraft.
One of the prime design considerations and problems in connection with outboard motors is the provision of an adequate exhaust system that permits relatively free breathing, good silencing, and also which ensures that excess heat is not generated and transmitted to other components of the outboard motor. Silencing an outboard motor presents a significant problem in that the length of the exhaust system is substantially limited by the compact nature of the structure. Generally, it has been known to utilize one or more expansion chambers formed in the drive shaft housing and lower unit for assisting in the silencing of the exhaust gases.
It is has also been known in outboard motor construction to discharge the exhaust gases to the atmosphere through the body of water in which the watercraft is operating, at least when the engine is operating at higher engine speeds. By utilizing an underwater exhaust gas discharge, the silencing of the exhaust gases can be augmented.
However, the use of the underwater discharge provides certain problems in that there is a concern that water may be ingested into the engine through the exhaust system. This is a particular problem in connection with two-cycle engines because of the firing impulses and the existence of negative pressures in the exhaust under some circumstances during operation. It has been proposed, therefore, to employ a watertrap arrangement that assists in ensuring against ingestion of water into the engine through the exhaust system.
Additionally, in the interest of obtaining good exhaust emission control, catalysts have been proposed for use in the exhaust system. The catalyst, however, causes additional resistance to the flow of exhaust gases through the exhaust system. Additionally, the catalyst should be protected from water so as to avoid damage. This presents other problems in connection with the location of the related components. It has been proposed also to position the catalyst at an upstream location from the watertrap device so as to ensure protection from water.
For example, with reference to FIGS. 1 and 2, an outboard motor 10 which includes a known exhaust system 12 is shown therein. As is typical with outboard motor practice, the outboard motor 10 includes a powerhead portion 14 with a drive shaft housing and lower unit portion 16 which depends from the powerhead 14.
The powerhead 14 includes an internal combustion engine 18. The engine 18 is surrounded by a protective cowling, which includes an upper cowling portion (not shown) and a lower tray portion 20.
The engine 18 is mounted in the outboard motor 10 such that its crankshaft 22 rotates about a vertically-extending axis. The crankshaft 22 drives a drive shaft 24 which is journaled within the drive shaft housing and lower unit portion 16.
The drive shaft 24 depends into the lower unit portion where it drives a propeller 26 via a conventional bevel gear reversing transmission 28. The propeller 26 is affixed to a propeller shaft 30 which is driven by the transmission 28. As such, as the drive shaft rotates and drives the transmission 28, the propeller 26 rotates to thereby propel an associated watercraft through the body of water in which it operates.
The drive shaft housing and lower unit 16 includes an upper case portion 32 which is generally open at its upper end. This open upper end is closed by an exhaust guideplate 34 which also supports the engine 18.
A pair of damper members 36 support the exhaust guideplate 34 and the upper case 32, respectively, relative to a steering or xe2x80x9cswivelxe2x80x9d shaft 38. The steering shaft is supported by a bracket assembly 40 which, in turn, is connected to the transom of an associated watercraft in a known manner.
The exhaust system 12 of the engine 18 includes an exhaust manifold (not shown) which defines at least a portion of a main exhaust passage that extends from the combustion chambers of the engine 18 into an expansion chamber 42. The main exhaust passage extends through the exhaust guideplate 34 and through an outlet end 44 thereof. The expansion chamber 42 aids in quieting the noises traveling through the main exhaust passage along with the exhaust gases.
The exhaust system 12 also includes a catalyst device 46 disposed in an outlet 48 of the expansion chamber 42. The catalyst device 46 is positioned in the outlet 48 such that substantially all of the exhaust gases flowing into the outlet 48 from the expansion chamber 42 passes through the catalyst device 46. The outlet 48 of the expansion chamber 42 extends through the exhaust guideplate 34 into an upper or a xe2x80x9criserxe2x80x9d exhaust passage 50.
With reference to FIG. 2, the riser portion 50 has a generally inverted U-shape. An outlet end 52 of the riser portion 50 connects to a further exhaust passage 54 which extends through the exhaust guideplate 34. An additional exhaust pipe 56 is connected to the exhaust passage 54 and extends downwardly through the upper case 32 toward the lower case 33.
With reference to FIG. 1, the lower case 33 includes a passage 58 which connects the exhaust pipe 56 with an exhaust discharge 60 which is positioned within the propeller 26.
Additionally, at least a portion of the exhaust system 12 is cooled by water drawn from the body of water in which the outboard motor 10 is operating. For example, the riser section 50 includes a cooling jacket 62. Additionally, the outboard motor 10 includes a temperature sensor 64 for sensing a temperature of the coolant flowing through the cooling jacket 62. The outboard motor 10 can also include an oxygen sensor 66 which includes an inner end exposed to the exhaust gases flowing through the riser pipe 50. The output from the oxygen sensor can be used to control an engine operating parameter such as those relating to fuel injection duration and timing and/or ignition timing.
In operation, exhaust gases generated in the combustion chambers within the engine 18 are directed downwardly by the main exhaust passage into the outlet end 44. Exhaust gases from the outlet end 44 flow into the expansion chamber 42 which thereby attenuates some of the noise associated with the exhaust gases.
All of the exhaust gases from the expansion chamber 42 flow through the catalyst device 46 and upwardly into the riser pipe 50. With reference to FIG. 2, exhaust gases flow upwardly into the riser portion 50 and laterally toward the port side of the outboard motor 10, then downwardly into the exhaust pipe 56. As shown in FIG. 1, exhaust gases from the exhaust pipe 56 flow into the exhaust passage 58 formed in the lower unit housing 33 and through the discharge 60 formed on the propeller 26. Thus, exhaust gases are further quieted by being discharged below the water surface level of the body of water in which the outboard motor 10 is being operated. Additionally, by directing the exhaust gases upwardly into the riser portion that is disposed above the exhaust guideplate 34, the riser portion 50 forms a watertrap which helps in preventing water from flowing upwardly through the exhaust pipe 56, through the riser pipe 50, and making contact with the catalyst device 46.
One aspect of the present invention involves the realization that an important benefit of the use of catalytic devices for marine engines is operative only during idling or low speed operation. In particular, marine engines without catalytic devices generate a significant amount of smoke during operation. Such smoke is caused by the adhesion of water molecules to unburned hydrocarbons in exhaust gases of the marine engine, such as an outboard motor. When such a marine engine associated with a watercraft, is operating at idle or low speed, the smoke generated with the exhaust gases tends to float in the vicinity of the watercraft, thereby creating an unpleasant environment for the passengers within the watercraft. In contrast, at high speed operation, sufficient wind is generated to flush the smoke associated with the exhaust gases rearwardly and away from the watercraft such that passengers do not notice such smoke.
In accordance with the present aspect of the invention, it has been discovered that while catalyst devices are particularly beneficial in eliminating unburned hydrocarbons and smoke generated during idling and low speed operation of a marine engine, such a benefit is moot during high speed operation. Thus, a marine engine can be provided with a lower capacity or smaller catalyst device which treats exhaust gases during idling that is not necessarily used to treat all of the exhaust gases during high speed operation.
In accordance with another aspect of the invention, an outboard motor includes an internal combustion engine with an engine body defining at least one combustion chamber. The outboard motor also includes a main exhaust passage configured to guide exhaust gases from the combustion chamber to an exterior of the engine body. The main exhaust passage includes an outlet end communicating with an expansion chamber. A branched exhaust passage extends from the main exhaust passage at a point upstream from the outlet end. The outboard motor also includes a catalytic device, wherein the branch passage connects the catalytic device with the main exhaust passage.
By including the catalytic device that is connected to the main exhaust passage by a branched exhaust passage, the outboard motor according to the present aspect of the invention can operate without forcing all of the exhaust gases to pass through the catalytic device. Thus, the outboard motor can operate with reduced back pressure in the exhaust system. Additionally, the outboard motor can operate, at low speeds, such as idling, for example, but without limitation, and direct all of the exhaust gases during such operation through the catalytic device, thereby preventing the generation of smoke. As such, a smaller catalytic device can be used, thereby reducing the weight and cost of the outboard motor.
In accordance with yet another aspect of the present invention, an outboard motor includes an engine having an engine body defining at least one combustion chamber. The outboard motor also includes an exhaust system comprising a main exhaust passage and an expansion chamber. The main exhaust passage includes an inlet end communicating with the combustion chamber and an outlet end communicating with the expansion chamber. An exhaust guideplate supports the engine above the expansion chamber. The main exhaust passage extends through the exhaust guideplate. An exhaust valve is supported by the exhaust plate and configured to control a flow of exhaust gases through the main exhaust passage.
By providing the outboard motor with a valve supported by the exhaust guideplate and configured to control the flow of exhaust gases through the main exhaust passage, the flow of exhaust gases through the exhaust system can be altered. For example, the exhaust valve can be opened under one operating condition and closed under another, as desired.
In accordance with yet another aspect of the present invention, an internal combustion engine having an engine body defines at least one combustion chamber. An exhaust manifold includes an inlet end receiving exhaust gases from the combustion chamber. A main exhaust passage is configured to guide exhaust gases from the exhaust manifold to the atmosphere. A branched exhaust passage includes an inlet end extending from the main exhaust passage. Additionally, the engine includes an exhaust valve disposed in the main exhaust passage downstream from the inlet end of the branched exhaust passage. The exhaust valve is configured to affect a relative proportion of exhaust gases flowing through the main exhaust passage and the branched exhaust passage.
According to a further aspect of the present invention, an internal combustion engine includes an engine body defining at least one combustion chamber. The engine also includes an exhaust system configured to discharge exhaust gases from the combustion chamber to the atmosphere. The exhaust system includes a catalyst device assembly comprising a catalyst housing and a cylindrical catalyst element having a longitudinal axis and being disposed in the housing. The housing includes a flange extending generally parallel to the longitudinal axis of the catalyst element.
These and other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiments disclosed.